Date of Graduation

Spring 2019

Degree

Master of Science in Geospatial Sciences

Department

Geography, Geology, and Planning

Committee Chair

Robert Pavlowsky

Keywords

Engineered Log Structures, large woody debris, log jam, catastrophic flood, stream restoration, Ozark Highlands

Subject Categories

Environmental Indicators and Impact Assessment | Geomorphology | Natural Resources and Conservation | Water Resource Management

Abstract

Engineered log structures (ELSs) composed of local tree logs have been installed in river channels throughout the Pacific Northwest as a restoration technique. However, ELSs have not been tested for use in the Ozark Highlands until recently. In October 2016 the U.S. Forest Service installed four ELSs to stabilize banks along the North Fork of the White River in Ozark County, Missouri. The purpose here is to report on monitoring studies of pre- and post-restoration channel conditions and to assess geomorphic responses to floods. Over a ten-day period in April 2017 there were two bankfull floods, and on April 30, 2017 a catastrophic flood event classified as a >500-year flood occurred with a stage of 12.8 m that was greater than 4 m above the previous record flood in 1985. The flood toppled the riparian forest and caused geomorphic changes throughout the study reach. Key findings of this study are: 1) One structure was buried by greater than 3 meters of bar sediment, 2) large woody debris pieces more than doubled from 96 pieces in 2016 to 209 pieces in 2017 in the 1,100 m reach where ELSs enhanced recruitment, 3) a planform change occurred where the thalweg migrated to the opposite side of the channel, and 4) Structures 3 and 4 trapped fluvial wood and enhanced sedimentation in targeted areas on a lateral bar feature. Conclusions of this study are: 1) During the high-magnitude flood, the floodplain acted as a point-bar where floodplain chutes were carved and sediment deposited over the normal floodplain surface; 2) Structures 3 and 4 enhanced LWD recruitment by creating flow separation between the channel and the mouth of a floodplain chute; 3) Managers should incorporate shallow bedrock typically present in the Ozarks into future ELS designs and; 4) Cables helped ELS logs remain in their installed location due to the added shear resistance. The use of ELSs in this research were designed to recruit fluvial wood and enhance sedimentation under more frequent flow conditions but withstood a historic flood. Therefore, further investigation is needed to determine suitability of using ELSs in Ozarks streams under lower magnitude, more frequent flows.

Copyright

© Joseph S. Nash

Open Access

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